The 'holding bin' concept is a way to narrow down the identification of an observation, if it can not be determined on species level but more specific than a 'formal taxon' would allow.
E.g. sister species would otherwise only be determined on genus level.

Use the observation field Holding bin (true bugs) when you want to specify a complex of multiple taxa.

Examples of use for this observation field:
Carpocoris purpureipennis/pudicus
Lygaeus equestris/simulans

See also the concept here: Holding bin (spider) (with a more comprehensive explanation)
and here: Holding bin (plants)